In this context, polishing refers to a step that is performed in connection with the straightening of a knife's edge, comprising an operation to zero in the outermost, comparatively thin edge of a sharpened knife blade by the use of a smooth steel tool. This step is normally performed manually by repeatedly moving the knife's edge along a straight and smooth steel tool in a cutting motion, towards and away from the operator, such that both sides of the knife is alternately brought into contact with the steel tool, while ensuring that the knife's contact angle with the steel tool is accurate and the same for both sides of the knife being polished. If the knife is applied at an angle that is incorrect, or too large, there is a significant risk of bending the edge from one side to the other, eventually resulting to a broken edge. Naturally, the manual procedure leads to varying results and requires a certain amount of skill to be acquired, in order to repeatedly achieve satisfying results.
A sharpening apparatus is known from U.S. Pat. No. 5,478,272, comprising arcuate steel members supported in one end to pivot from a base member. The steel bars are biased, and crossing each other in front of a slot formed in the base member. The knife's edge is pressed manually towards the steel members and pulled lengthwise through the slot, while forcing the point of intersection between the steel members always to contact the knife's edge, independently of the contact pressure from the knife. The apparatus is stationary and arranged to be fastened onto a work surface.
A knife in use is subjected to mechanical forces that effect the straightness of the knife's edge and thus reduces the effectiveness of the knife. For this reason, the knife's edge is normally straightened several times between successive operations for sharpening the edge. Thus, the manual polishing procedure may be seen as time consuming and labor-intensive, requiring repeated movements of the arms in frequent polishing operations.
The present invention aims to improve prior methods by providing a polishing tool that leads to repeatable results without requiring special skills to be acquired by the operator, and more specifically with respect to the contact angle between polishing tool and the two sides of the knife blade.
Another object is to provide a time- and laborsaving polishing tool of high capacity.
These and other objects are met in a tool according to the features and characterizing portion of claim 1. Embodiments are specified in subordinated claims.
According to the invention there is provides a polishing tool driven for rotation. The polishing tool comprises two oppositely positioned and co-rotating rings of elongate honing studs, extended at intersecting directions forming an angle (α) wherein the knife's edge is inserted to be straightened by the rotating polishing tool.